The invention relates to a crankcase for a piston engine or piston compressor including a bearing support structure for supporting a divided crankshaft main bearing which has a bearing part formed integrally with the bearing support structure and a bearing cover bolted to the bearing part.
Proper operation of the drive mechanism of a piston machine requires high rigidity of the crankcase and particularly of the bearing support structure in order to have the least possible form changes by external forces effective during operation.
DE OS 42 27 125 discloses a crankcase for a piston internal combustion engine including bearing support structures for mounting divided main bearings of a crankshaft and a crankshaft casing wall extending down below the crankshaft axis and connected to the bearing support structures above the crankshaft axis. The main bearing of the crankshaft comprises a bearing half disposed in the bearing support structure and a bearing cover bolted to the bearing support structure by bearing bolts screwed into heavy-walled threaded bolt holes.
The rigidity of the crankcase, or respectively, the bearing support structure is achieved by an accumulation of wall material in the area of the bolt mounting structures and the joint area between the crankcase wall and the bolt mounting structure adjacent the bearing support structure at the end remote from the crankshaft bearing and by providing reinforcement ribs on the outside of the crankcase wall and the bearing support structure. However, the utilization of such a large amount of material is contradictory to the need for light-weight crankcases.
DE OS 33 05 731 discloses a crankcase for a multi-cylinder piston type internal combustion engine with walls which extend transversely to the longitudinal engine axis and which support each a divided main bearing for the crankshaft. The main bearing consists of a bearing base portion associated with the wall and a bearing cover which is mounted onto the bearing base portion by bolts which are screwed into heavy walled bolt mounting columns. The crankcase wall extends down to an area below the crankshaft axis to about the level of the bolt heads and is connected to the bearing base portion by means of a web extending about at the level of the dividing plane of the main bearing. In addition to these webs the piston forces of the engine transmitted from the crankshaft to the main bearings are transferred to the crankcase through the bolt mounting columns in various areas of the wall which includes the main bearings. The location of these areas depend on the size of the transverse component of the piston force vector. Consequently, the rigidity of the crankcase is determined by the wall thickness of the walls supporting the main bearings. These walls must be quite strong and consequently heavy in order to provide the rigidity needed for the bolt mounting columns and the bolts received therein to remain unaffected by the transverse component of the piston force vector.
It is therefore the object of the present invention to provide a crankcase which has a relatively low weight but is still capable of withstanding relatively high dynamic loads.